1. Field of Invention
This invention pertains to a sensor for mounting in motor vehicles for sensing a crash, said sensor generating a signal for deploying a passenger restraint system such as an air bag.
2. Description of the Prior Art
Air damped crash sensors have become widely adopted by many of the world's automobile manufacturers to sense that a crash is in progress and initiate the inflation of an air bag or tensioning of seat belts. These sensors are constructed from a ball and tube such as disclosed in U.S. Pat. Nos. 3,974,350; 4,198,864; 4,284,863; 4,329,549 and 4,573,706.
The ball-in-tube sensor currently in widespread use has a magnetic bias. Both ceramic and Alnico magnets are used depending on the amount of variation in bias force caused by temperature that can be tolerated. Sensors used in the crush zone of the vehicle and safing or arming sensors used both in the crush zone and out of the crush zone, use ceramic magnets since they can tolerate a wide variation in bias force. Alnico magnet are used for the higher biased non crush zone discriminating sensors where little variation in the bias can be tolerated. If a spring bias is used in place of the magnetic bias as shown in Thuen U.S. Pat. No. 4,580,810, the variation in the bias force with temperature can be practically eliminated.
In the conventional ball-in-tube sensor, two cantilevered contacts are bridged by the ball and both the ball and the contacts may be gold plated to minimize the contact resistance. If the sensing mass instead of bridging the contacts pushed one contact into another, the gold plating on the ball could be eliminated.